Due to the characteristics of thin profile and low power consumption, liquid crystal displays (LCDs) are widely used in electronic products, such as portable personal computers, digital cameras, projectors, and the like. Generally, LCD panels are classified into transmissive, reflective, and transflective types. A transmissive LCD panel uses a back-light module as its light source. A reflective LCD panel uses ambient light as its light source. A transflective LCD panel makes use of both the back-light source and ambient light.
As known in the art, a color LCD panel 1 has a two-dimensional array of pixels 10, as shown in FIG. 1. Each of the pixels comprises a plurality of sub-pixels, usually in three primary colors of red (R), green (G) and blue (B). These RGB color components can be achieved by using respective color filters. FIG. 2A illustrates a plan view of a pixel 10 in a conventional transflective liquid crystal panel. The pixel 10 is divided into three color sub-pixels 12R, 12G and 12B and each sub-pixel can be divided into a transmission area (TA) and a reflection area (RA). The pixel 10 is associated with a gate line, Gate n. The color sub-pixels 12R, 12G and 12B are separately associated with data lines DataR m, DataG m and DataB m. The color filter for use with a pixel 10 is shown in FIG. 2B. In FIG. 2B, the color filter has three color filter sections R, G, B corresponding to the color sub-pixels 12R, 12G, 12B of the pixel 10. A cross sectional view of a color sub-pixel 12 is shown in FIG. 3. As shown, the color sub-pixel 12 has an upper layer structure, a lower layer structure and a liquid crystal layer 200 disposed between the layer structures. The upper layer structure comprises an upper substrate 110, a color filter 120 and an upper electrode 130. The lower layer structure comprises a lower substrate 170, a device layer 160, a passivation layer 150 and an electrode layer. The electrode layer comprises a reflective electrode 142 in the reflection area electrically connected to the device layer through a via 152, and a transmissive electrode 144 in the transmission area electrically connected to the reflective electrode 142. The transmissive electrode 144 and the upper electrode are made from a transparent material such as indium-tin oxide (ITO). The reflective electrode 142 also serves as a reflector and is made from one or more highly reflective metals such as Al, Ag, Cr, Mo, Ti and AlNd.
If the overall reflectivity in the reflection areas is insufficient to produce a desired color density, voids or colorless filters within the color filter sections in the reflection areas are used to increase the reflectivity, as shown in FIG. 2B. With this color correction method, the color image quality of the LCD panel may not be desirable.
It is thus advantageous and desirable to provide a method and a sub-pixel structure for use in a transflective color LCD panel for increasing the reflectivity in the pixel without unduly degrading the color quality of the panel.